In general the function of a circuit breaker is to electrically engage and disengage a selected circuit from an electrical power supply. This function occurs by engaging and disengaging a pair of operating contacts for each phase of the circuit breaker. The circuit breaker provides protection against persistent overcurrent conditions and against the very high currents produced by short circuits. Typically, one of each pair of the operating contacts are supported by a pivoting contact arm while the other operating contact is substantially stationary. The contact arm is pivoted by an operating mechanism such that the movable contact supported by the contact arm can be engaged and disengaged from the stationary contact.
There are two modes by which the operating mechanism for the circuit breaker can disengage the operating contacts: the circuit breaker operating handle can be used to activate the operating mechanism; or a tripping mechanism, responsive to unacceptable levels of current carried by the circuit breaker, can be used to activate the operating mechanism. For many circuit breakers, the operating handle is coupled to the operating mechanism such that when the tripping mechanism activates the operating mechanism to separate the contacts, the operating handle moves to a fault or tripped position.
To engage the operating contacts of the circuit breaker, the circuit breaker operating handle is used to activate the operating mechanism such that the movable contact(s) engage the stationary contact(s). A motor coupled to the circuit breaker operating handle can also be used to engage or disengage the operating contacts. The motor can be remotely operated.
A typical industrial circuit breaker will have a continuous current rating ranging from as low as 15 amps to as high as 1600 amps. The tripping mechanism for the breaker usually consists of a thermal overload release and a magnetic short circuit release. The thermal overload release operates by means of a bi-metalic element, in which current flowing through the conducting path of a circuit breaker generates heat in the bi-metal element, which causes the bi-metal to deflect and trip the breaker. The heat generated in the bi-metal is a function of the amount of current flowing through the bi-metal as well as for the period of time that that current is flowing. For a given range of current ratings, the bi-metal cross-section and related elements are specifically selected for such current range resulting in a number of different circuit breakers for each current range.
In the event of current levels above the normal operating level of the thermal overload release, it is desirable to trip the breaker without any intentional delay, as in the case of a short circuit in the protected circuit, therefore, an electromagnetic trip element is generally used. During the short circuit condition operation of the circuit breaker gas and plasma is generated as the contacts in the circuit breaker move apart. Such gasses are directed into an arc chute for expulsion outside of the circuit breaker. That expulsion usually occurs at or near line terminals which can damage the cable connection, the terminals themselves or cause arcing on a pole-to-pole or pole-to-ground basis as the gas and plasma exit the circuit breaker. In addition, accidental contact with the live connectors of the circuit breaker should be avoided by the operator or installer of the circuit breaker. Further, it is desirable to reduce the likelihood that a small object accidentally dropped, for example a bolt or a nut, could become lodged underneath the breaker terminals in a manner that would reduce electrical clearances.
Thus, there is a need for a terminal barrier system that will protect the circuit breaker terminals from the gasses generated during a short circuit operation of the circuit breaker. There is also a need to provided a terminal barrier system that prevents pole to pole electrification. There is a further need to provide a barrier terminal system that prevents accidental contact with the live electrical connections in a circuit breaker. There is a further need for a terminal barrier system that will help prevent small objects from accidentally becoming lodged underneath the breaker terminals. Further, there is a need for a terminal barrier system that has interchangeable parts to accommodate a range of continuous current ratings of circuit breakers.